In manufacturing processes, it is common to move goods along by means of conveyor systems having straight and curved sections. In many instances, it is desirable that the curved sections be of a small radius, such as to turn at almost a right angle in a confined space. Such curved conveyor sections typically have a continuous loop conveyor belts or may have an articulated linked conveyor belt.
Typically, such curved conveyor belts are driven through the use of a linked drive chain, a linkless drive chain, or a drive belt, each of which has a looped length and is typically driven by an electric motor. The most common way to drive a curved conveyor belt is through the use of a linked drive chain. For the sake of simplicity and clarity, only a linked drive chain will be referred to in this background section. The drive chain is in the form of a continuous loop, as is the conveyor belt, and is disposed at the outer edge of the conveyor belt or along the middle of the conveyor belt and directly drives the conveyor belt.
In order to facilitate proper meshing of the drive chain and conveyor belt, the drive chain must follow the path of the conveyor belt so as to keep the drive chain at the same speed as the conveyor at all points along the conveyor. Accordingly, the loop of the drive chain is essentially oriented similarly to the loop of the conveyor belt. In other words, since the conveyor belt is oriented substantially horizontally, the rollers at the ends of the conveyor belt are also oriented substantially horizontally. In order for the drive chain to follow the path of the conveyor belt, the axes of the links of the drive chain and the end roller's drive sprockets, which are engaged by the drive chain, must both be oriented substantially horizontally. In this manner, the drive chain can articulate vertically around the drive sprockets.
However, in order for a drive chain to follow the same curved path as a curved conveyor belt, it must also bend horizontally along its length, transversely to its usual direction of articulation between adjacent links. Conventional chains cannot bend significantly in a direction transverse to their normal direction of articulation between adjacent links, simply due to their construction. The minimum radius that a conventional chain can bend to in such a transverse direction is perhaps about ten feet, which is far too large a radius to be used in many curved conveyors. Further, a conventional drive chain is severely stressed by such transverse bending. Special flexible drive chains that can bend transversely to their normal direction of articulation may be used, but they are more expensive than conventional chains and still have a limited radius of curvature of perhaps four to five feet, which is larger than is often required as some conveyor bends must be quite sharp, perhaps with an outside radius of about two to three feet.
Another important consideration, irrespective of what type of drive chain is used, is that the drive sprocket on the rollers of the conveyor belt must have the same pitch diameter as the diameter of the rollers on the conveyor belt in order to provide for speed matching of the drive chain and conveyor belt. Such drive sprockets typically have a minimum pitch diameter of about three inches, more or less, as dictated by the drive chain. Accordingly, the minimum diameter of the end roller of a curved conveyor belt is also about three inches, more or less. An end roller having a three inch diameter would cause a significant cleft at the end of the curved conveyor, where the curved conveyor meets another conveyor. It is highly desirable to minimize such clefts in order to facilitate the smooth transfer of articles, especially readily damageable articles, from the curved conveyor to the next conveyor. It is therefore preferable to have the end rollers of a curved conveyor as small a diameter as possible, perhaps about one-half inch, or even less, which cannot be accomplished by presently known curved conveyors driven by drive chains unless an auxiliary end roller is also used.
Another manner of driving a curved conveyor belt, specifically a continuous and unbroken type curved conveyor belt, which overcomes some of the problems encountered with a drive chain arrangement, is to drive one or both of the two end rollers that the conveyor belt is looped around, typically by means of an electric motor. This manner of driving a curved conveyor belt also has significant disadvantages associated with it. The conveyor belt must be in tension in order to permit the driving force from the end roller or end rollers to be frictionally transmitted to the curved conveyor belt. In order to have the curved conveyor belt uniformly in tension and the curved conveyor belt must therefore be manufactured to very close tolerances, which is difficult and expensive, and therefore is undesirable. Moreover, such curved conveyor belts stretch and therefore require frequent adjustment or replacement. Further, it is difficult to transport heavy loads using this type of drive mechanism as it requires frictional engagement of the end roller or end rollers with the curved conveyor belt. Also, where articles such as food products are being conveyed, oils tend to become deposited on the conveyor belt, thus potentially causing reduced friction between the drive roller or drive rollers and the conveyor belt.
Another method of driving a curved conveyor belt, specifically a continuous and unbroken type curved conveyor belt, and which also overcomes some of the problems encountered with a drive chain arrangement, is to have a portion of the curved conveyor belt pinched between an external auxiliary drive roller and an opposed idler wheel that is spring biased against the drive wheel. This type of drive mechanism does not work well because the drive belt is driven at only one point along the belt. Again, where articles such as food products are being conveyed, oils tend to become deposited on the conveyor belt, thus potentially causing reduced friction between the external auxiliary drive roller and the conveyor belt.
It can therefore be seen that not using a drive chain arrangement to drive a curved conveyor belt is often unacceptable.